The present invention relates to a liquid enzyme cleaning composition in which the enzyme is stable at alkaline pH and in the presence of water at concentrations of at least about 60 weight percent. The present enzyme cleaning composition typically yields superior soil (especially protein soil) removal properties. In one embodiment, the composition of the invention stabilizes the enzyme with potassium borate.
A major challenge of detergent development for industry, restaurants, and homes is the successful removal of soils that are resistant to conventional treatment and the elimination of chemicals that are not compatible with the surroundings. One such soil is protein, and one such chemical is chlorine or chlorine yielding compounds, which can be incorporated into detergent compounds or added separately to cleaning programs for protein removal. Protein soil residues, often called protein films, occur in all food processing industries, in restaurants, in laundries, and in home cleaning situations.
In the past, chlorine has been employed to degrade protein by oxidative cleavage and hydrolysis of the peptide bond, which breaks apart large protein molecules into smaller peptide chains. The conformational structure of the protein disintegrates, dramatically lowering the binding energies, and effecting desorption from the surface, followed by solubilization or suspension into the cleaning solution. The use of chlorinated detergent is not without problems, such as harshness and corrosion. In addition, a new issue may force change upon both the industry, consumers, and detergent manufacturers: the growing public concern over the health and environmental impacts of chlorine and organochlorines.
Detersive enzymes represent an alternative to chlorine and organochlorines. Enzymes have been employed in cleaning compositions since early in the 20th century. However, it took years of research, until the mid 1960""s, before enzymes like bacterial alkaline proteases were commercially available and which had all of the minimum pH stability and soil reactivity for detergent applications. Patents issued through the 1960s related to use of enzymes for consumer laundry pre-soak or wash cycle detergent compositions and consumer automatic dishwashing detergents. Early enzyme cleaning products evolved from simple powders containing alkaline protease to more complex granular compositions containing multiple enzymes to liquid compositions containing enzymes. See, for example, U.S. Pat. No. 3,451,935 to Roald et al., issued Jun. 24, 1969 and U.S. Pat. No. 3,519,570 to McCarty issued Jul. 7, 1970.
Liquid detergent compositions containing enzymes have advantages compared to dry powder forms. Enzyme powders or granulates tended to segregate in these mechanical mixtures resulting in non-uniform, and hence undependable, product in use. In dry compositions, humidity can cause enzyme degradation. Dry powdered compositions are not as conveniently suited as liquids for rapid solubility or miscibility in cold and tepid waters nor functional as direct application products to soiled surfaces. For these reasons and for expanded applications, it became desirable to have liquid enzyme compositions.
Although water is a desirable solvent for liquid cleaning compositions, there are problems in formulating enzymes into aqueous compositions. Enzymes generally denature or degrade in an aqueous medium resulting in the serious reduction or complete loss of enzyme activity. This instability results from at least two mechanisms. Enzymes have three-dimensional protein structure which can be physically or chemically changed by other solution ingredients, such as surfactants and builders, causing loss of catalytic effect. Alternately when protease is present in the composition, the protease will cause proteolytic digestion of the other enzymes if they are not proteases; or of itself via a process called autolysis. The prior art discloses attempts to deal with these aqueous induced enzyme stability problems by minimizing water content or altogether eliminating water from the liquid enzyme containing composition. See, for example, U.S. Pat. No. 3,697,451 to Mausner et al. issued Oct. 10, 1972 and U.S. Pat. No. 4,753,748 to Lailem et al. issued Jun. 28, 1988.
In order to market an aqueous enzyme composition, the enzyme must be stabilized so that it will retain its functional activity for prolonged periods of (shelf-life or storage) time. If a stabilized enzyme system is not employed, an excess of enzyme is generally required to compensate for expected loss. However, enzymes are expensive and are in fact the most costly ingredients in a commercial detergent even though they are present in relatively minor amounts. Thus, it is no surprise that various methods of stabilizing enzyme-containing, aqueous, liquid detergent compositions are described in the patent literature. There remains a need, however, for additional methods and compositions for stabilizing enzymes in cleaning compositions, particularly at high concentrations of water and alkaline pH.
The present invention relates to a liquid enzyme cleaning composition in which the enzyme is stable at alkaline pH and in the presence of water at concentrations of at least about 60 weight percent. The enzyme cleaning composition preferably employs potassium borate to stabilize one or more enzymes at these conditions of pH and water concentration. The present composition maintains stability of the enzyme at alkaline pH, which preferably falls in the range of about 8 to about 11, preferably greater than about 9, preferably about 9 to about 10, preferably about 9.3. The present composition maintains stability of the enzyme at concentrations of water up to about 85%, preferably in the range of about 60% by weight to about 85% by weight water, preferably about 60% by weight to about 70% by weight water, preferably 62% by weight to 69-72% by weight water.
In an embodiment, the liquid enzyme cleaning composition includes a surfactant, a detersive enzyme, a boric acid salt, and at least about 60% by weight water, formulated to retain about 100% of the detersive enzyme""s initial activity at ambient temperature for at least about 11 months after forming the composition. In an embodiment, the liquid enzyme cleaning composition includes a surfactant, a detersive enzyme, a potassium borate, and at least about 60% by weight water. In an embodiment, the liquid enzyme cleaning composition includes a surfactant, a detersive enzyme, a boric acid salt, and at least about 80% by weight water.
Potassium borate is a preferred boric acid salt in each of these embodiments. Potassium borate is preferably present in an amount effective to provide significant stabilization of the enzyme compared to compositions without potassium borate at the same concentrations of water. Potassium borate can be present at about 10 or 15 weight percent. Preferably, after forming the present liquid enzyme cleaning composition including potassium borate, the detersive enzyme retains about 100% of its initial activity for at least about 11 months at ambient temperature. Preferably, after forming the present liquid enzyme cleaning composition including potassium borate, the detersive enzyme retains at least about 80% of its initial activity at 100xc2x0 F. for at least about 50 days after forming the composition. Preferably, after forming the present liquid enzyme cleaning composition including potassium borate, the detersive enzyme retains at least about 50% of its initial activity at 120 OF for at least about 25 days after forming the composition.
The present composition can stabilize one or more of a variety of enzyme. Detersive enzymes that can be employed in the present compositions include a protease, an amylase, a lipase, a cellulase, a peroxidase, a gluconase, or a mixture thereof. Preferably the detersive enzyme is a protease, an amylase, a lipase, or a mixture thereof. Preferred proteases include an alkaline protease, such as a subtilisin. Preferred amylases include an endoamylase. Preferred lipases include a lipolase.
The composition can also include additional ingredients such as a source of calcium ions, a polyol, a builder, a dye, or a combination thereof. Preferably, the present composition includes an amphoteric surfactant, a protease, an amylase, and/or a lipase, potassium borate, calcium chloride, propylene glycol, citric acid salt, and a dye. Preferably these ingredients are present at about 8% by weight surfactant, about 2% by weight protease, about 10% to about 15% by weight boric acid salt, about 0.25% by weight calcium chloride, about 8% by weight propylene glycol, about 4% to about 7% by weight citric acid salt, and about 0.02% by weight dye.